In a case where temperatures of high-temperature objects such as a metal molten pool which is formed during welding and its peripheral area, or metals during heat treatment, a boiler, and the inside of a blast furnace are measured, a contact-type temperature probe which is a general temperature detector may not be able to be installed. Alternatively, even in a case where a temperature probe can be installed, the temperature probe detects the temperature at its installation point. For this reason, there is a possibility that a temperature distribution on a wide range of surfaces cannot be ascertained.
A noncontact-type optical temperature measurement method is known as means for solving such circumstances. In the optical temperature measurement method, an image is acquired using thermography, a near-infrared camera, a visible light camera or the like, and the temperature distribution of an object to be measured is obtained by the acquired image. In this case, the temperature of the object to be measured is detected using thermal radiation (radiated light) from the object to be measured. A relationship between radiated light and temperature is subject to a relational expression known as the Planck's equation, and thus in further consideration of emissivity specific to substance, it is possible to determine a temperature from the intensity of radiated light (luminance of radiated light).
Since the intensity of radiated light changes drastically due to even a slight difference in temperature, high-accuracy measurement can be made. However, there is a possibility that the temperature of the object to be measured is not able to be accurately measured in a situation in which a heat source is close to an object to be measured due to intensive radiated light from the heat source serving as noise.
For example, in a case where the heat source is a TIG torch, and the object to be measured is a melting portion of a weld object, a TIG electrode is located at a position close to the melting portion (molten pool and the periphery of the molten pool), and furthermore emits intensive radiated light at high temperature. For this reason, radiated light from the TIG electrode is reflected from the melting portion, and the reflected radiated light serves as noise, which leads to the possibility of an accurate temperature not being able to be measured.
As a method for solving such circumstances, it is considered to make observation from a direction in which radiated light from the heat source is not reflected. However, since a camera to be used is large in size and has a restriction on its installation position, the camera is likely not to be installed at an appropriate position. In addition, when an image is captured by the camera, it is also considered to shield the radiated light from the heat source. However, temperature measurement is disturbed even in a case where the amount of leakage of the radiated light is slight, and thus a high degree of accuracy is required for the installation of a light shielding member.
Patent Document 1 discloses a temperature information measurement method for excluding the influence of disturbance light by selecting three or more sets of wavelengths, each set including two wavelengths, of the amount of radiation radiated from a test object, detecting the intensity of the amount of radiation at two wavelengths for each set, executing relative temperature calculation while sequentially adding or subtracting the numerical value of the amount of radiation equivalent to each wavelength to or from each measured radiation value, and setting a temperature when a temperature value obtained from two or more expressions reaches an allowable range to the temperature of the test object.
PTLs 2 to 4 also disclose a device that measures a temperature.